Question: Simplify the following expression: $k = \dfrac{1}{2a} - \dfrac{5}{8a}$
Answer: In order to subtract expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $2a$ and $8a$ $\lcm(2a, 8a) = 8a$ $ k = \dfrac{4}{4} \cdot \dfrac{1}{2a} - \dfrac{1}{1} \cdot \dfrac{5}{8a} $ $k = \dfrac{4}{8a} - \dfrac{5}{8a}$ $k = \dfrac{4 -5}{8a}$ $k = \dfrac{-1}{8a}$